Thursday, May 9, 2013

Sigma 35 1.4 Preliminary Review

Here is an update on my impressions of the Sigma 35 1.4, which is currently the sharpest lens for Nikon full frame cameras, as measured by DXO.

BACKGROUND
A while back, I tried the Nikon 28 1.8G, and while I liked the sharpness, contrast and the flare resistance, I was disappointed by the autofocus performance of my copy. Here is that review.

I decided to try instead the Sigma 35 1.4, one of the new lenses from Sigma's revamped Global Vision lineup. The Sigma 35 1.4 has a reputation for being exceptionally sharp. In addition, because of the slightly wider aperture and longer focal length, I would get a shallower depth of field. Here is a comparison between the DOF and perspective of the 28 1.8G and the Sigma 35 1.4.

That was almost two months ago, so here's an update.

SHARPNESS

f/1.4

The Sigma 35 1.4 is indeed as sharp as others have found, both in terms of resolution and acuity. Even wide open at f/1.4, it reveals every tiny detail.

f/1.4

DEPTH OF FIELD
Another good thing about the Sigma is that on a full frame, using the Sigma wide open is actually feasible. With my Sigma 50 1.4, the DOF was usually too shallow and I had to stop down to f/2.0 to get a usable DoF. Not so with the Sigma 35 1.4 which I like using wide open. At f/1.4, the DoF is just shallow enough to make subjects stand out from the background.

f/1.4

For shots with two or more people, if I really want all subjects to be in focus, then yes I do stop down. When I do, the Sigma is even sharper, although for web-sized viewing, the increased sharpness is not likely to be noticeable (because it's already sharp at f/1.4).

f/2.0

f/1.4

Speaking of shallow DoF, I found the bokeh to be very smooth. And even though the Sigma has two aspheric elements, I have not seen any onion bokeh.

f/1.4

CHROMATIC ABERRATION
Hardly any chromatic aberration visible. Yes there's a little bit of spherochromatism but practically every wide aperture lens has it too (and I personally don't find it distracting).

FLARE RESISTANCE
With respect to flare resistance, I thought the Sigma was pretty good though I was more impressed with the flare resistance of the 28 1.8G. I don't recall seeing any flare blobs in any of my shots although I know the Sigma is not immune from them (I can occasionally see them when I point the lens at certain angles to the light). As for the kind of flare that reduces the contrast, it can happen with the Sigma, as in this backlit shot (using the Sigma on a D7000).

AUTOFOCUS
You recall that one of the reasons I got the Sigma instead of the Nikon 28 1.8G is due to autofocus. First, the easy part - the Sigma focuses very quickly and is totally silent. As for accuracy, here is my honest opinion: the Sigma is sadly not perfect either. I definitely got more keepers than my copy of the Nikon 28 1.8G, but I found the accuracy of the autofocus to be somewhat spotty. Usually the focus is close enough to be usable but only around 50% of my shots are at critical focus (at f/1.4). That is better than the 28 1.8G I tested which was around 20%. I don't think it's an issue with my D600 because by comparison, my Nikon 85 1.8G has very reliable autofocus wide open. I can use the 85 1.8G at f/1.8 all day long without worrying about whether I got the shot in focus.

A shot with less than critical AF

The inaccuracy of the autofocus is also not easy to correct with AF fine-tuning because it appears to be inconsistent. Sometimes it's accurate, sometimes not at varying distances. What usually ends up happening is I have to take a two or three shots, and one of them ends up having the correct autofocus. When I can, I also try to use contrast detection through live view (which avoids any front- or back-focusing errors), in which case I get a significantly higher percentage of shots in focus.

Fortunately, the new Sigma lenses can be customized using the reasonably-priced Sigma USB dock ($59), which will start shipping around May 20. The USB dock will allow adjustment of front and back focus at different focal lengths and different focusing distances. I have mine on order and am hoping that with it, I can make my Sigma 35 1.4 focus more accurately. I'll update this review when I receive the Sigma USB dock.